Chemical amplification positive resist compositions are materials that form patterns on substrates as follows. When irradiated with far ultraviolet radiation or the like, those resist compositions generate acids in the irradiated areas, and undergo reaction utilizing the acids as a catalyst to cause a difference in solubility in a developer between the areas unirradiated and irradiated with the actinic rays, thereby enabling pattern formation.
In the case where KrF excimer laser is an exposure light source, resins containing as their basic skeletons poly(hydroxystyrene) showing weak absorption in the region of 240 nm are used as a main component. Therefore, such resist compositions have high sensitivity and can form good-quality patterns at high resolution, compared with traditional resist compositions containing naphthoquinone-diazide/navolak resin combinations.
However, when light sources of shorter wavelengths, such as ArF exceimer laser (193 nm), are used for exposure, even the aforementioned resist compositions of chemical amplification type are not satisfactory, because compounds having aryl groups intrinsically show strong absorption at wavelengths around 193 nm.
On the other hand, utilization of poly(meth)acrylate as a polymer showing weak absorption in the region of 193 nm is described in J. Vac. Sci. Technol., B9, 3357 (1991). However, that polymer has a problem of being inferior to conventional phenol resins having aryl groups in resistance to dry etching generally carried out in the fabrication process for semiconductors.
In keeping with the recent trend toward finer patterning and higher throughput, it becomes increasingly important to reduce errors caused by exposure. The hitherto known resist compositions have narrow exposure margin and bad line edge roughness, which are impediments to heighten throughput.
Further, the recent finer patterning results in the aspect ratio being strict about the coating thickness also, and so the patterns formed have a tendency to topple easily. This tendency is observed noticeably in the cases of ArF resist, electron beam (EB) resist, vacuum ultraviolet (VUV) resist and extremely short ultraviolet (EUV) resist. Herein, the term “toppling of patterns” is intended to include all pattern-toppling phenomena regardless of what are their causes, e.g., whether the phenomenon is induced by lack of adhesion or coating strength.